1. Field of the Invention
The present invention relates to a multiple-input multiple-output wireless communication system. More particularly, the present invention relates to an apparatus and a method for an uplink beamforming and an uplink Space-Division Multiple Access (SDMA) based on the beamforming in a multiple-input multiple-output wireless communication system.
2. Description of the Related Art
The rapid growth of the wireless mobile communication market has resulted in a greater demand for various multimedia services in a wireless environment. Recently, to provide such multimedia services, which include a large amount of transmit data and increased data delivery rate, research is being conducted on Multiple Input Multiple Output (MIMO) wireless communication systems that provide a more efficient use of limited frequencies.
A MIMO wireless communication system can transmit a signal over independent channels per antenna and thus increase transmission reliability and data rate without the use of an additional frequency or additional transmit power, compared to a single-input single-output system. The MIMO system can be extended to a MIMO system in a multi-user environment supporting a plurality of users. That is, the MIMO system in the multi-user environment enables the multiple users to share spatial resources ensured by the multiple antennas, thus further improving the spectral efficiency.
A Spatial Multiplexing (SM) of the MIMO wireless communication system techniques builds a plurality of spatial subchannels between one transmitter and one receiver and independently transmits data per spatial subchannel, to thus raise the data transmission capacity in each link. A Space Division Multiple Access (SDMA) technique can increase the transmission capacity of the system by transmitting data signals to multiple receivers at the same time. Provided that a Base Transceiver Station (BTS) includes nT-ary transmit/receive antennas and an Access Terminal (AT) includes nR-ary transmit/receive antennas, the BTS can use the nT-ary transmit antennas and the AT can use the nR-ary receive antennas for downlink SM and SDMA, and the AT can use the nR-ary transmit antennas and the BTS can use the nT-ary receive antennas for uplink SM and SDMA.
However, unlike the BTS that is not limited in its use of power, the AT is subject to a power limitation. Hence, the AT cannot use a plurality of Radio Frequency (RF) transmit chains which consume considerable power, such as a power amplifier, at the same time to maximize the power efficiency. Accordingly, to overcome the power limitation of the AT and adopt the SM and the SDMA, there is a need for an apparatus and a method for performing the SDMA using a single RF receive chain at the AT.